2012 Volume 84 Issue 2 Pages 63-67
This study aimed to estimate the notch sensitivity of spheroidal vanadium carbide cast iron (SCI-VCrNi) in rotating bending fatigue test. We investigated the fatigue failure mechanism of SCI-VCrNi by comparison with FCD400 by fractography. As a result of fatigue test, the fatigue limit of SCI-VCrNi was found to be σw ＝ 350MPa, higher than FCD400. In addition, the notch factor and notch sensitivity of SCI-VCrNi was less than FCD400. As a result of observing the crack initiation points of SCI-VCrNi, the cluster of VC was found to be dominant. We then quantified the cluster of Vanadium Carbide (VC) using the √area parameter model, and as a result, confirmed that the notch specimen's √area was smaller than that calculated for smooth specimens.
Moreover, the stress intensity factor range (ΔK) taking into account the considered stress concentration of notch specimens was higher than the smooth specimens. For this reason, the small clusters of VC were thought to become the crack initiation point in the notch specimen. We also observed a stripe pattern peculiar to cast iron in the fatigue state of the matrix, and thus studied the fracture surface of SCI-VCrNi. The results suggested that SCI-VCrNi in which crack progresses in the matrix has low notch sensitivity due to the low notch sensitivity of austenite steel. In addition, the VC of the fracture surface manifested broken and characteristic aspects, indicating that crack progresses in the matrix while breaking VC when the crack reaches VC, and as a result, VC becomes resistant to crack growth.
